#include <gtest/gtest.h>

class Circle {
public:
    explicit Circle(const int radius)
        : radius_(radius), area_(M_PI * radius * radius) {}
    friend class CircleTest;
    FRIEND_TEST(CircleTest, Area);

private:
    int radius_;
    double area_;
};

TEST(CircleTest, Area) {
    const Circle circle(5);
    EXPECT_DOUBLE_EQ(circle.area_, 78.539816339744831);
}